Method of making electron tubes



Jan. 4, 1966 PL A. DE BACKER METHOD 'OF MAKING ELECTRON TUBES Filed Sept. 18, 1961 I NVEN TOR. /w/i/y A24 0:54:41;

United States Patent 3,227,506 METHOD OF MAKTNG ELECTRON TUBES Lucien P. A. De Backer, Middletown, N.J., assignor to Radio Corporation of America, a corporation of Delaware Filed Sept. 18, 1961, Ser. No. 138,946 6 Claims. (Cl. 316Z) My invention relates to a method of making electron tubes, and particularly concerns the solution of certain problems presented in the manufacture and testing of electron tubes having a flashable getter.

The gettering of electron tubes is accomplished by releasing within a tube envelope after or during evacuation thereof a gas-absorbing material such as barium. The barium so released, usually impinges upon adjacent wall portions of the tube envelope, producing a silvery deposit on such portions, which can be seen from the tube exterior when the envelope is made of glass, but which is shielded from sight when the tube envelope includes an opaque portion such as a metal, surrounding the getter. In glass envelope tubes, the presence of even a small deposit is a qualitative indication that the getter has flashed. The magnitude of the deposit provides a quantitative measure of the barium released, from which it can be determined whether a satisfactory flash has occurred. However, in tubes having an opaque envelope portion around the getter structure, no ready indication is available either qualitative or quantitative, that the getter has flashed.

One reason for a qualitative failure of a getter flash is the difliculty in determining the exact magnitude of heating current through the getter structure required for a satisfactory flash. Such determination is critical for satisfactory results. Thus, an excessive current magnitude may generate such a high heat in a getter sheath or trough, as to melt the same. This results in a splashing of the molten sheath or trough metal within a tube envelope and a depositing of the metal on tube elements Whose functions are adversely affected thereby. At the other extreme is a current magnitude of such small value as to be insufficient to heat the getter material to a temperature at which any getter flash occurs at all.

It has not been feasible heretofore to overcome this difliculty satisfactorily. While the amount of heating current is capable of variation within a relatively wide range, it has not been apparent how to control such variation to produce a current magnitude adequate for desired getter flash but below that at which such heat is gen .erated that the trough or sheath melts. No matter what current magnitude is employed, the length of time up to a certain point, that the getter structure is energized by the current affects the temperature produced therein. The length of time that the current passes through the getter structure can be varied readily, but here again the desired control of such variation has not been feasible.

Applicant has found that the problem of control of current and time in a getter flashing operation is due primarily to the fact that getter structures do not have uniform dimensions. This lack of uniformity from getter to getter, renders it impossible to rely on a predetermined control of the flashing current and time of application, for flashing successive getters. For some getter structures the predetermined control may result in a satisfactory flash, but for others it may produce either an underflash or an overflash, as mentioned in the foregoing.

Getter making techniques lack that high order of precision that assures such exact uniformity in length and cross-sectional area of the getter structures as to permit satisfactory reliance on a predetermined getter flashing current and time duration of its application.

In addition to the balance of strict structural uniformity from getter to getter, a further factor adversely affecting ice a reliance on a fixed flashing current and time, involves the manner in which the getter is supported in a tube. In tubes where the getter is energized by current fed to its holder by lead-ins, end portions of the getter structure are usually fixed to the lead-ins in a suitable manner, such as by welding. It is not feasible to control exactly the spacing of the lead-ins from the free ends of the getter structure. Thus, variations in length of the getter structure lportion between the lead-ins are common. While such variations may be relatively slight, they are suflicient to produce objectionable erratic heat responses to a fixed heating current and time.

It is thus apparent, that it is desirable to control the time and current magnitude in relation to unpredictable structural variations of a getter, in a getter flashing operation.

Furthermore, in instances where it may not be practical to provide this-type of control, it is desirable to provide a convenient testing technique to determine the adequacy of a prior getter flash, particularly in tubes having an opaque envelope portion surrounding the gettter structure. Electron tubes are usually subjected to tests immediately after manufacture and getter flashing, but these tests are made to determine whether the tubes meet certain initial criteria. Such tests do not usually indicate whether getters in the tubes have flashed properly.

Accordingly, it is an object of my invention to provide an improved method of making electron tubes.

It is another object to provide an improved method of flashing getters of electron tubes.

A further object is to provide an improved method of testing the adequacy of a getter flash.

One feature of the invention involves simultaneously flashing a getter within the tube and measuring the adequacy of the flash. Another feature concerns providing an indication of the occurrence, and measuring the completeness, of a getter flash, as a separate operation. In accordance with my method, a portion or element in the tube adjacent the getter structure-is connected to a suitable voltage source so that the getter sructure and this tube element act in diode fashion with each other. For example, barium remaining in or on the getter structure when heated during and after the flash emits electrons which, with appropriate applied voltage, and with the getter structure suitably oriented in diode fashion in relation to the adjacent portion or element aforementioned, are collected thereby. The resultant current may be fed through a suitable indicating device such as an ammeter, which is calibrated to indicate the magnitude of the current flow, which provides an indication of getter flash. According to one feature of the invention, when the testing operation accompanies a getter flash, and the measuring device detects a predetermined amount of current flow, further energization of the getter structure is stopped. According to another feature, if the test is made after a supposed flashing of the getter, current is continually drawn from the getter structure until the dial on the indicating device stops at a reading determined by the amount of emission from the getter structure, which depends on whether the getter is flashed or not, thereby affording a reliable indication of whether the getter actually flashing or not. It should be noted that this latter testing step may have no effect on the getter flash, since a practice of this step requires the getter structure to be heated only to a temperature at which barium emits electrons, which is appreciably below the temperature used for flashing the getter. The former temperature is, of course, much lower than that at which the trough or sheath melts.

Further objects and advantages of the invention will become apparent as the present description continues.

In the drawing, to which reference is now made for a more detailed description of one example of the inventron,

FIG. 1 is an elevational view in section of an electron tube, in the manufacture of which the invention may be practiced advantageously;

FIG. 2 is a sectional view of a lower fragment of the tube shown in FIG. 1, and rotated axially 90, to more clearly show the getter and its manner of support;

FIG. 3 shows a cross-section of the getter structure of FIG. 2, taken along the line 33 of FIG. 2;

FIGS. 4a and 4b are transverse sectional views of other getter structures with which the invention may be used;

FIG. 5, shows a socket in section, that may be used to effect desired electrical connection to lead-ins on which the getter structure is mounted; and

FIG. 6 is a schematic circuit diagram showing one way in which the invention may be carried out.

An electron tube, in the manufacture of which my invention is particularly useful, is shown in FIG. 1. This tube is a so-called Pencil type and comprises an anode 10, a grid 12, and a tubular cathode 14 energized by a heater 16. The anode 10 is supported in a tubular anode terminal 18. The grid 12 is mounted on an electrically conducting disc 20. The cathode 14 is fixed to a sleeve 22 telescoped within a tubular cathode terminal 24. One end of anode terminal 18 is sealed to one end of a relatively short tube 26 made of an insulating material such as glass or ceramic. One end of the cathode terminal 24 is sealed to one end of a relatively short tube 28, made of an insulating material. The grid disc has opposite faces thereof sealed near its periphery to the free ends of the short tubes 26, 28. The elongated envelope thus provided is closed att one end by a stem 30 made of insulating material such as glass or ceramic, and the other end is sealed by a pinching off of the exhaust tubulation 32. The heater 16 is connected to leads 34, 36 passing through the stem 30.

Within the cathode terminal 24, and shielded from view by the opaque metal of which this terminal is made, is mounted a getter structure 38. The manner in which the getter structure 38 is mounted is shown more clearly in FIG. 2. Thus, end portions 40, 42 of the getter structure are fixed, as by welding, to end portions of the two lead-in conductors 44, 46 sealed through stem 30 and terminating in relatively short stubs 48, 50. The heater terminals or prongs 52, 54, extend an appreciable greater distance from the exterior face of stem 36, than do the stubs 48, 50, as shown in FIGS. 1 and 2.

The getter structure shown in FIGS. 1 and 2 is depicted in greater detail in FIG. 3. It comprises a trough 56 having exposed getter material 58 therein. In this example, the getter material consists of a compound containing barium and which is not adversely affected by exposure to the ambient atmosphere during handling prior to incorporation in the tube. Well known compounds of getter material of this type are barium berylliate and barium titanate. When this material is heated to a temperature of about 1000 C., a chemical reaction takes place that liberates the barium. The release of the barium occurs rapidly and in a fiashable manner. The compound temperature is raised by heating the trough by current losses therein, produced by connecting the stubs 48, '50 across a source of electrical current of approximately four amperes, at a relatively low voltage of one or two volts. The trough is made of a material having a relatively high electrical resistance, such as tantalum for effective heating thereof by the current losses therein.

The invention may also be practiced in connection with other getter structures some of which are shown in FIGS. 4a and 4b. The getter structure of FIG. 4a comprises a sheath 60 of nickel having a zone of weakness 62 and enclosing a getter material 64. Due to the protection afforded by the closed sheath 60, this material 64 may be pure barium. In FIG. 4b a sheath 66 of iron overlaps at 68 to provide a zone of weakness in the sheath, while fully enclosing the material 70, which may be pure barium. In these examples, a heating of sheaths 60 and 66 causes the barium therein to generate sufiicient pressure to rupture the zones of weakness described, and to erupt from the sheath in the form of a flash.

The getter structure 38 is so oriented within the tube that its flash is directed to a region wherein it is harmless to tube operation. In the instant example, such direction is towards the inner wall of cathode support sleeve 22.

To prevent getter material from reaching the inner surface of stem 30 and thereby result in electrical leakage between the heater leads 34, 36, a disc 72, which may be made of an insulating material such as mica, is positioned adjacent to the stem 30, as shown in FIGS. 1 and 2.

It has been found by applicant that during and after a getter flash, some of the barium released by the flash remains in the trough or sheath. This fact is taken advantage of in the following example of the novel method.

In practicing applicants method in a simultaneous getter flashing and measuring operation the getter structure 38 within an evacuated envelope 39, is heated to flashing temperatures by a power source 74 (FIG. 6) connected to the ends of the getter structure 33- by means of leads 76, 78. The leads 76, 78 may be conveniently connected to the stubs 48, 50 shown in FIG. 2, by means of a socket 80 shown in FIG. 5. The socket includes conductive sleeves 82, 84 having an inner diameter for snugly receiving the studs 48, 50, and is provided with tabs 86, 88 connected to leads 76, '73. Slugs 90, 92 within the sleeves, limit the degree of penetration of the stubs into the sleeves and since the slugs prevent any appreciable entrance of the longer heater prongs 52, 54 into the sleeve, they provide a convenient orienting means. An opening 94 through the socket receives the heater prongs referred to. In this example described, the power source 74 produced a current output of about four amperes at a voltage of about two volts.

During the flashing operation, some free barium remains in or on the trough 56 at the getter structure. This barium is at a sufficiently high temperature to emit electrons readily to a suitable collector. Such collector is provided, by connecting the cathode terminal 24, and the cathode support sleeve 22 which it contacts, to a positive voltage source 96 of about volts, by means of a lead 98 connected to the cathode terminal 24, as shown in FIG. 2. Between the voltage source 96 and the lead 98 is an ammeter 100 having milliampere calibrations on the face thereof. A resistor 102 of about 10,000 ohms serves to protect the ammeter from power surges. The negative side of the voltage source 96 is connected in parallel to lead 78 serving the getter structure 38, and to the negative side of the current source 74.

Under these conditions, emission current from the heated free barium on the getter structure 33 Will be collected by collector 22, 24 and an indication of the current magnitude will be provided by the ammeter 100. Applicant has found under the conditions specified, that when the ammeter indicates a current flow of 0.4 milliampere, the flashing of the getter has been accomplished successfully. The circuit energizing the getter is then opened by opening a switch 104.

The opening of switch 104 to terminate further heating of the getter structure may be accomplished automatically, by means of a photocell, not shown, responsive to the position of the ammeter dial at a reading of 0.4 milliampere, or by other means responsive to this current, to actuate a suitable relay, not shown, associated with the switch.

In another example of the method of the invention, the sleeve 22 and terminal 24 or any other convenient element of the tube in the path of the getter flash, may serve as the cathode, and the getter 38 may be connected to the collector potential. In this Way, if a getter flash has occurred, the barium coating on the element or sleeve 22 will be electron emissive in response to a suitable temp a to which the element or sleeve 22 may be raised, as by R.F., for example.

In either example, where a getter of the sheath typ'es shown in FIGS. 4a and 4b is used, a flashing current of about amperes should be employed.

Furthermore, while the source of current 74 and the source of voltage 96, are shown in the form of batteries, these sources may comprise alternating current means, such as of sixty cycle frequency.

It is, of course, to be understood that the getter structure 38 may be flashed inductivity by R.F., instead of being directly connected to a source of current. Thus, where the envelope portion surrounding the getter is made of material that is free from magnetic shielding properties such as ceramic, the getter may be conveniently flashed by RF. This manner of flashing can be practiced in conjunction with the measuring and testing steps described in the foregoing.

If it is desired to employ themeasuring or testing aspect of the invention apart from and subsequent to a getter flashing operation, the current source 74 may have a smaller value than for flashing. Such smaller value may be about two amperes. However, it is feasible to use the same current source of about four amperes for getter 38, and about 15 amperes for the getters shown in FIGS. 4a and 4b, both for getter flashing and for a subsequent test to determine whether the getter has flashed adequately. When the flashing and measuring steps are carried out simultaneously, there is no need for a subsequent testing step.

The foregoing examples have involved three different types of getter structure used in Pencil type tubes. While the structure shown in FIGS. 1 and 2 requires about four amperes for getter flashing, the structures shown in FIGS. 4a and 4b require about fifteen amperes for this purpose. This diflerence in current requirement is due to a diflerence in the electrical resistance of the structures. However, in each case the emission current indicating a good flash is about 0.4 milliampere. This may be explained by the fact that each of the three types of getters described contain about the same amount of getter material, and the indicated reading of about 0.4 milliam-p'ere has been found by applicant to evidence a satisfactory getter flash. It is believed that for other getter types of about the same getter material yield that characterizes the getter structures described, the emission current in the amount mentioned is a satisfactory evidence of a desirable getter flash.

Where a more critical quantitative measurement of the getter material yield is desired, as for getter types diflering appreciably in size from types discussed, the amount of emission current indicating a sastisfactory getter flash can be determined empirically by persons skilled in the art. However, where the getter material is exothermic in nature, a complete getter flash is certain to have taken place regardless of the size and shape of the getter structure, if there is any evidence at all of emission current during a practice of the method of the invention.

I claim:

1. Method of making an electron tube having an envelope, a getter within said envelope, and a metal element within said envelope, said method comprising evacuating said envelope to a relatively low pressure, heating said getter for flashing said getter while maintaining a potential diiference between said getter and metal element suflicient to cause emission current to flow between said getter and element after said getter has flashed, and stopping said heating of the getter when said emission current reaches a predetermined flash-indicating magnitude.

2. In a method of making an electron tube having a flashable getter, the steps comprising heating said getter to a temperature at which it normally flashes, and simultaneously measuring the emission current flowing between the getter and a metal element adjacent thereto within the tube, and stopping said heating of the getter when said current reaches a predetermined flash-indicating magnitude.

3. Method of flashing a getter within an electron tube comprising heating said getter to flashing temperature, producing a potential dilference between said getter and a metal element adjacent to the getter within said tube to cause emission current to flow between said getter and element when said getter has flashed, and stopping the heating of said getter when said emission current has reached a predetermined flash-indicating magnitude.

4. Method of flashing a getter structure wherein said structure comprises a metal support and a flashable electron emission getter material in contact with said support, said method comprising the steps of heating said support to a temperature at which said getter material normally flashes, connecting said support and a metal element adjacent thereto in diode fashion to produce emission current flow between said support and element, measuring said current flow, and stopping said heating of said support when said current flow reaches a predetermined flash-indicating magnitude.

5. A combined getter flashing and flash measuring method comprising simultaneously heating a barium containing getter to a temperature at which it normally flashes to release barium, collecting the released barium on a first metal element, producing a potential difference between said first element and a second metal element of sufficient magnitude to cause emission current to flow from said first element to said second element, and stopping the heating of said getter when said current has reached a predetermined flash-indicating magnitude.

6. In a method of making an electron tube having a getter structure surrounded by an opaque member, the steps of heating said structure to a temperature at which electron emissive getter material therein normally flashes, producing a potential difference between said getter structure and a wall of said member adjacent to said getter structure, whereby emission current flows between said structure and wall, and stopping the heating of said structure when said current reaches a predetermined flash-in dicating magnitude.

References Cited by the Examiner UNITED STATES PATENTS 2,332,428 10/1943 Atlee et a1 316-25 X 2,838,708 6/1958 Yoder 31625 X 2,979,371 4/1961 Spalding 324 20 X FRANK E. BAILEY, Primary Examiner.

WALTER L. CARLSON, Examiner.

G. S. KINDNESS, Assistant Examiner. 

1. METHOD OF MAKING AN ELECTRON TUBE HAVING AN ENVELOPE, A GETTER WITHIN SAID ENVELOPE, AND A METAL ELEMENT WITHIN SAID ENVELOPE, SAID METHOD COMPRISING EVACUATING SAID ENVELOPE TO A RELATIVELY LOW PRESSURE, HEATING SAID GETTER FOR FLASHING SAID GETTER WHILE MAINTAINING A POTENTIAL DIFFERENCE BETWEEN SAID GETTER AND METAL ELEMENT SUFFICIENT TO CAUSE EMISSION CURRENT TO FLOW BETWEEN SAID GETTER AND ELEMENT AFTER SAID GETTER HAS FLASHED, AND STOPPING SAID HEATING OF THE GETTER WHEN SAID EMISSION CURRENT REACHES A PREDETERMINED FLASH-INDICATING MAGNITUDE. 